Simply passing GHC options to ghc-mod check command.

Check.hs

@@ -24,5 +24,5 @@ check opt fileName = withGHC $ checkIt `gcatch` handleErrMsg
         setTargetFile file
         load LoadAllTargets
         liftIO readLog
-    options = ["-Wall","-fno-warn-unused-do-bind"]
+    options = ["-Wall","-fno-warn-unused-do-bind"] ++ ghcOpts opt
            ++ map ("-i" ++) (checkIncludes opt)

GHCMod.hs

@@ -26,7 +26,7 @@ usage =    "ghc-mod version 0.6.2\n"
         ++ "\t ghc-mod list [-l]\n"
         ++ "\t ghc-mod lang [-l]\n"
         ++ "\t ghc-mod browse [-l] [-o] <module> [<module> ...]\n"
-        ++ "\t ghc-mod check [-i inc] <HaskellFile>\n"
+        ++ "\t ghc-mod check [-g GHC options] [-i inc] <HaskellFile>\n"
         ++ "\t ghc-mod type <HaskellFile> <module> <expression>\n"
         ++ "\t ghc-mod info <HaskellFile> <module> <expression>\n"
         ++ "\t ghc-mod lint [-h opt] <HaskellFile>\n"
@@ -39,6 +39,7 @@ defaultOptions :: Options
 defaultOptions = Options {
     convert = toPlain
   , hlintOpts = []
+  , ghcOpts = []
   , checkIncludes = []
   , operators = False
   , packageConfs = []
@@ -52,6 +53,9 @@ argspec = [ Option "l" ["tolisp"]
           , Option "h" ["hlintOpt"]
             (ReqArg (\h opts -> opts { hlintOpts = h : hlintOpts opts }) "hlintOpt")
             "hint to be ignored"
+          , Option "g" ["ghcOpt"]
+            (ReqArg (\g opts -> opts { ghcOpts = g : ghcOpts opts }) "ghcOpt")
+            "extra GHC options"
           , Option "o" ["operators"]
             (NoArg (\opts -> opts { operators = True }))
             "print operators, too"

Types.hs

@@ -13,6 +13,7 @@ import GHC.Paths (libdir)
 data Options = Options {
     convert   :: [String] -> String
   , hlintOpts :: [String]
+  , ghcOpts   :: [String]
   , checkIncludes :: [String]
   , operators :: Bool
   , packageConfs :: [FilePath]

elisp/ghc-flymake.el

@@ -13,6 +13,7 @@
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (defvar ghc-hlint-options nil "*Hlint options")
+(defvar ghc-ghc-options nil "*GHC options")
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
@@ -45,18 +46,17 @@
   (let ((after-save-hook nil))
     (save-buffer))
   (let ((file (file-name-nondirectory (buffer-file-name))))
-    (list ghc-module-command (ghc-flymake-command file ghc-hlint-options))))
+    (list ghc-module-command (ghc-flymake-command file))))
 
 (defvar ghc-flymake-command nil) ;; nil: check, t: lint
 
-(defun ghc-flymake-command (file opts)
+(defun ghc-flymake-command (file)
    (if ghc-flymake-command
-       (let ((hopts (ghc-mapconcat (lambda (x) (list "-h" x)) opts)))
+       (let ((hopts (ghc-mapconcat (lambda (x) (list "-h" x)) ghc-hlint-options)))
 	 `(,@hopts "lint" ,file))
-     (if (null ghc-flymake-check-includes)
-         (list "check" file)
-       (let ((includes (ghc-mapconcat (lambda (x) (list "-i" x)) ghc-flymake-check-includes)))
-         `("check" ,@includes ,file)))))
+     (let ((gopts (ghc-mapconcat (lambda (x) (list "-g" x)) ghc-ghc-options))
+	   (includes (ghc-mapconcat (lambda (x) (list "-i" x)) ghc-flymake-check-includes)))
+       `(,@gopts "check" ,@includes ,file))))
 
 (defun ghc-flymake-toggle-command ()
   (interactive)